1. Field of the Invention
The present invention relates to a gradation correction curve producing method and a gradation correction curve producing apparatus for producing a gradation correction curve to correct gradation of an image, and a gradation correction curve producing program storage medium storing a gradation correction curve producing program, when executed in a computer, which causes the computer to operate as the gradation correction curve producing apparatus.
2. Description of the Related Art
Hitherto, it is performed that image data is taken into a personal computer and the like to be subjected to an edition of an image on the image data, and the image data subjected to the edition is subjected to a color conversion to meet characteristics of an image output apparatus of interest, such as a color printer, and further subjected to a gradation correction and the like, and then the image data is outputted to the image output apparatus so that the image output apparatus outputs a desired image.
In the personal computer and the like, the various sorts of processing as mentioned above are performed. particularly, in the gradation correction processing, there is performed such a processing that a gradation correction curve is defined in form of an LUT (look-up-table) for each of monochromes of for example cyan (C), magenta (M), yellow (Y) and black (K), and the image data of CMYK are converted in accordance with the associated gradation correction curves, respectively.
To make up such a gradation correction curve, the personal computer or the like is used to produce image data representative of a color chart consisting of a plurality of density patches on each of C, M, Y and K, and the image data thus produced are fed to an image output apparatus such as a color printer so that the image output apparatus outputs a color chart. Densities of density patches of C, M, Y and K constituting the outputted color chart thus outputted are measured. Association of the density measurement result of the density patches thus obtained with the values of the image data when the density patches are produced makes it possible to make up the gradation correction curve.
Basically, the gradation correction curves are able to be made up in the manner as mentioned above. However, the gradation correction curves thus made up are considered only in a color axis direction of C, M, Y and K, and thus are not always completely adjusted with respect to a gray direction consisting of a combined color of three colors of C, M and Y. In view of the foregoing, according to the prior art, the gradation correction curve is determined in such a manner that image data representative of a gray of density patch consisting of a combined color of C, M and Y is printed out through performing a gradation correction using the gradation correction curve made up once in the manner as mentioned above, the gradation correction curve is fine-controlled through evaluating a color of the gray density patch, it is determined whether gradations of monochromes of C, M and Y are within a specified tolerance and the color of the gray is also within the specified tolerance as a result of the fine-control, and the fine-control is repeated over and over so that both the monochromes and the gray offer the specified tolerance. In this case, as mentioned above, the fine-control is repeated over and over. This takes a lot of times and labors to finally obtain a gradation correction curve with great accuracy, and it needs an expert to obtain a gradation correction curve with great accuracy.